Pompey stormed to their first League One victory of the season with a clinical display at Leyton Orient.
They had a comfortable interval lead after crosses from Joe Rafferty were converted by Marlon Pack and Colby Bishop.
And John Mousinho's side then went further ahead just after the break, as Omar Beckles sliced a Gavin Whyte delivery into his own net.
Kusini Yengi then continued his bright start to life with the Blues, coming off the bench to convert and penalty and wrap up a 4-0 rout.